Who Should Be Suspected?
During poliovirus outbreaks, most infected patients remain asymptomatic or have mild, self-limited disease. A minority of patients (<2%), however, develop paralytic poliomyelitis or occasionally meningitis or encephalitis without paralysis. Illness may be preceded by fever, myalgias, and nonspecific “viral” symptoms.
Poliomyelitis is caused by infection of the anterior horn cells of the spinal cord, resulting in acute flaccid paralysis of associated muscle groups. Spinal poliomyelitis may vary in severity from isolated paresis to paralysis of the limbs, quadriplegia, and paralysis of the diaphragm or other muscle groups. Cranial nerve nuclei may be involved resulting in bulbar poliomyelitis, with paralysis of muscles involved in swallowing or destruction of cells regulating central respiration. Infected patients may develop disease related to both spinal and bulbar poliomyelitis. Cerebral function is typically unaffected.
Five to ten percent of patients die, usually as a result of respiratory failure. Most children recover; however, a majority are left with residual sequelae ranging in severity from mild motor weakness to complete paralysis.
Laboratory Findings
Poliomyelitis may be suspected on the basis of clinical signs and symptoms in appropriate clinical settings.
Culture
: The diagnosis is usually confirmed by isolation of virus in culture. Several samples of stool and throat for viral culture, obtained at least 24 hours apart, should be collected early in the course of disease.
Serology of acute and convalescent sera
: May be submitted to support a diagnosis of poliomyelitis, but test interpretation may be difficult.
CSF findings
: Nonspecific. Cell count is usually 25–500/μL; rarely is normal or markedly elevated. At first, most are PMNs; after several days, most are lymphocytes. Protein may be normal at first, increased by 2nd week (usually 50–200 mg/ dL), and normal by 6th week. Glucose is usually normal.
Core laboratory
: Blood shows early moderate increase in WBC (≤15,000/μL) and PMNs. WBC returns to normal within 1 week. Increased AST in 50% of patients is caused by the associated hepatitis.
RESPIRATORY VIRUSES
See Chapter
13
, Respiratory, Metabolic, and Acid–Base Disorders, for a detailed discussion of viral respiratory tract pathogens, including adenovirus, influenza viruses, parainfluenza viruses, and RSV.
RUBELLA (GERMAN MEASLES)
Definition
Rubella virus causes German measles, one of the classic viral exanthems of childhood (the “third disease”). The virus primarily infects the respiratory epithelial cells. Infection is transmitted by respiratory droplets. The virus has a global distribution, although endemic virus circulation has been greatly reduced or eliminated in countries with widespread vaccination programs. Humans are the only natural host.
Who Should Be Suspected?
Rubella infection is usually mild and self-limited. Viremia typically occurs after 5–7 days, and clinical infection may ensue around 14 days after exposure with a nonspecific “viral” syndrome, including fever, malaise, mild respiratory symptoms, and lymphadenopathy. The characteristic, nonconfluent rash starts on the face and then progresses to the trunk and extremities. The rash resolves in 3–5 days. Up to 50% of infected children may remain asymptomatic.
The congenital rubella syndrome is caused by transplacental infection of a fetus during the viremic phase of illness. Maternal infection early in gestation is associated with more severe disease (approximately 80% incidence with maternal rubella in the first trimester). Virtually, all fetal organ systems are susceptible to infection, and infection may lead to stillbirth or premature delivery. The most common anomalies include cardiac defects, cataracts and other ocular defects, deafness, bone defects, hepatitis, microcephaly and mental retardation, splenomegaly, and thrombocytopenia. Subacute arthritis is a common (70%) complication of rubella infection in adult women. Fingers, wrists, and knees are the most commonly affected joints, and symptoms may last up to 1 month.
Rubella is preventable by vaccination, with a primary goal of reducing the incidence of the congenital syndrome. Vaccine-induced protection may wane over time; improved vaccines have improved the durability of the immune response. Since 1993, 70% of patients with rubella fall into the 15- to 39-year age group, reflecting this declining immunity. Therefore, significant public health resources have been dedicated to ensuring that adolescents, especially girls, have been immunized.
